The invention relates to an electro-optical data transmission module with a laser light emitter chip and a light receiver chip.
Such a data transmission module is known, for example, from U.S. Pat. No. 5,864,468.
A difficulty when designing such modules is that, on the one hand, they should be able to cope with as high a data transmission rate as possible (500 Mbps and more), and on the other hand they should be as small as possiblexe2x80x94in particular also owing to their increased use in the electronics of consumer goods. These two requirements are difficult to reconcile. This is because, in the first instance, such high-rate modules require a robust design, for which reason, known modules are embodied with a housing which takes up a relatively large amount of space. A further reason which runs counter to the desired miniaturization is that the edge-emitting semiconductor lasers which are used in such modules at present have relatively high power requirements. For this reason, in order to avoid electronic crosstalk between the transmitter components and the receiver circuit it is necessary to maintain a certain minimum spacing. A third reason for the fact that conventional modules require a large amount of space is that the high power drain of the laser light emitter chip results in the need for special driver circuits for the conventional electro-optical data transmission modules. These driver circuits are generally arranged within the module housing and increase its overall size further.
The invention is based on the object of specifying an electro-optical data transmission module with a laser light emitter chip and a light receiver chip which is suitable for the optical transmission of data at data rates in the range of 500 Mbps (multimedia) and requires little space.
Accordingly, a significant aspect of the invention is that a surface-emitting laser light emitter chip is used as the transmitter component. Surface-emitting laser light emitter chips, so-called VCSELs (Vertical Cavity Surface Emitting Lasers), have a significantly lower power drain than comparable edge-emitting laser chips. As a result of the low power drain, the problem of electronic crosstalk is significantly reduced, i.e. the light receiver chip and the circuits (preamplifier, post-amplifier) connected downstream of it can be mounted closer to the transmitter circuit.
A further measure which is essential for the objective of the invention consists in the fact that both the surface-emitting laser light emitter chip and the light-sensitive light receiver chip are accommodated in separate SMT (Surface Mounting Technology) housings. This permits a compact, modular and mechanically stable design of the electro-optical data transmission module.
Both known measures (surface-emitting laser light emitter chip and individual SMT housings for the emitter chip and receiver chip) make it possible to provide an electro-optical data transmission module with a data transmission rate of approximately 500 Mbps and more and a high degree of miniaturization.
According to one particularly preferred embodiment, the electro-optical data transmission module comprises a securing means which mechanically connects the two SMT housings. The securing means may be, for example, a module housing which surrounds the two SMT housings and/or an attachment device arranged between the two SMT housings. In both cases, the securing means permits the first SMT housing to be adjusted with respect to the second SMT housing, i.e. permits the transmission light beam paths and reception light beam paths to be adjusted.
A further preferred refinement of the invention is characterized in that the data transmission module also comprises a light guide extension element which is accommodated in a third SMT housing. As a result, the modularity of the entire design is increased further.
The SMT housings are preferably parallelepiped-shaped or cuboid. A robust data transmission module according to the present invention can then be obtained by simply combining the housing cubes/parallelepipeds.
In an arrangement composed of a circuit board and an electro-optical data transmission module mounted on it, one advantageous embodiment is characterized in that a driver circuit for the surface-emitting laser light emitter chip is mounted outside the data transmission module on the circuit board. The relocation of the driver circuit outside the electro-optical data transmission module permits the module dimensions to be reduced, both by virtue of the saving in space which is achieved in this way and also by virtue of the reduction in the electronic crosstalk within the module.
A further arrangement of the data transmission module and circuit peripherals which is advantageous in terms of miniaturization is characterized in that a preamplifier circuit for the light-sensitive light receiver chip is arranged inside the second SMT housing, and in that a post-amplifier circuit for the light-sensitive light receiver chip is mounted outside the data transmission module on the circuit board. The saving in space is brought about by the relocation of the post-amplifier circuit.
Further preferred refinements of the invention are given in the subclaims.
The invention is explained in more detail below by means of an exemplary embodiment and variants of the same with reference to the drawing, in which: